With the rapid growth of commercial and military wireless communication systems, the need for compactness has increased. Antennas are considered a critical component of such wireless systems. The desire for compactness has reduced the available space for all of the antennas required on a mobile platform, which in turn has increased the desire for miniaturization of antennas.
Several approaches have been adopted for achieving antenna miniaturization including using different shapes or geometry, complex matching circuits, use of high dielectric constant materials, high temperature superconductors, or capacitive and/or inductive loadings. However, reducing the size of the antenna is typically achieved at the expense of bandwidth, gain, efficiency, and polarization purity, which results in poor antenna performance.
The development of a reconfigurable antenna (RA) is also desirable in wireless communication systems where space is limited, particularly in commercial and military wireless communication systems. For example, with an RA, the frequency, radiation pattern, and polarization of the antenna may be reconfigured, or changed, based on the requirements for different applications. Reconfigurable antennas have been found to be useful for many applications such as broadband or multiband wireless communication, multiple-input multiple-output (MIMO) systems, frequency hopping radar, cognitive radio, and filtering out reserved frequency band for narrowband wireless technology. In particular, it is desirable for a single reconfigurable antenna to achieve multi-functionality in order to replace multiple ordinary antennas with different functions, and to provide more degrees of freedom for adaptive communication systems.
However, while changing one characteristic of the antenna, another characteristic may also be affected and may be difficult to control. Frequency tunable antennas have been developed with a fixed main beam in the radiation pattern such that both polarization and frequency can be tuned simultaneously and independently for a slot-ring antenna. Many reconfigurable antennas have been achieved electronically by tuning the capacitance of varactor diodes or by switching the “on” and “off” state of PIN-diodes using DC biasing voltages. In addition, RF MEMS technology has been applied to antenna reconfiguration by using RF MEMS varactors and switches.
However, it would be desirable to develop an antenna for use in wireless communication devices which achieves both miniaturization and reconfiguration at the same time.